German patent document 3,643,519 filed Dec. 19, 1986 by H. Kiendl et al describes a control device for a mixing valve. The valve is servo-controlled and the servomotor in turn is controlled by a microprocessor receiving an input from a temperature sensor in the output conduit. The microprocessor is programmed at the factory, with the program burnt in so that it cannot be subsequently changed.
German patent document 3,600,383 based on a British priority of Jan. 16, 1985 by K. Ellington et al describes such a system with special safety functions that close the valve under certain circumstances, for instance if the temperature at the outlet runs out of control despite adjustment attempts. Once again this system is preprogrammed and not adaptable to field conditions.